1. The Field of Invention
The present invention relates to control of the change of trajectory of a motor vehicle and, more particularly, to a device for acting on the trajectory of a vehicle by electrical means.
2. The Related Art
In the current state of the art, the steering of a passenger motor vehicle is usually controlled by means of a steering wheel. The driver turns the steering wheel one way or the other in order to point the vehicle in one or the other direction. In this manner, the driver applies a yaw movement to the vehicle. In other respects, electrical control means for all of the actuators of a motor vehicle, and in particular the steering, are being developed to an increasing extent. This technology is known by the name xe2x80x9csteer by wirexe2x80x9d.
The technology for controlling actuators via an electrical link consists in replacing with electric links the linkages, which are generally hydraulic or mechanical at present, between the operating device and the actuators. For instance, as regards the steering of motor vehicles, the following system will be substituted for the traditional mechanical system, which may be assisted or unassisted, existing between the steering wheel and the steerable wheels. The steering operating component available to the driver of the vehicle may be a traditional steering wheel or a lever such as a joystick. At the road-wheel level, there is an electrical actuator, preferably an individual one for each road wheel. The instructions applied by the driver of the vehicle to his operating device are sent to the actuators via an electrical link, with the entire system being placed under the supervision of a direction controller loaded with programs suitable for driving the actuators appropriately.
The advantage of this technology is that it is ideally compatible with advances in electronics, which are making increasingly sophisticated feedback control systems possible; and which make it possible not only for the steering of the road wheels to be subject to the manual controls but also for the steering to be supervised by a safety system. For instance, the road wheels may be set to an angle which not only takes into account the instructions from the driver of the vehicle, but which also takes into account dynamic parameters observed in the vehicle.
When a driver wishes to change the trajectory of his vehicle, this may correspond to two requirements which are quite different in nature. The first requirement is to take a turn, in which case it is necessary to apply a yaw acceleration to the vehicle, followed by a phase in which the yaw rate varies little, then a yaw deceleration on exiting the turn, in order to obtain a direction of travel which is different after the maneuver compared with what it was before the maneuver. When overtaking a vehicle on a road or a motorway, it is known that the driver adjusts the steering wheel in order to apply a small turn to the left, in countries where vehicles are driven on the right, immediately followed by a small turn to the right after the vehicle has moved sideways to a sufficient extent. Lastly, to complete the overtaking maneuver, another small turn in order to change the orientation of the vehicle so as to rejoin the initial traffic lane, and finally a fourth small turn. It will therefore be understood that, in order to perform an overtaking maneuver, it is necessary to apply two transverse accelerations to the vehicle by means of four yaw accelerations. However, only the transverse accelerations are in fact useful for an overtaking maneuver in a straight line.
It is therefore an object of the present invention to provide an electrical system for controlling the trajectory of a vehicle, all of whose road wheels are steerable wheels, the steering angle being applied individually and selectively to each of the steerable wheels by a dedicated electrical actuator. The electrical system has an operating means, available to the driver for acting on the trajectory of the vehicle and further has a trajectory controller which determines a road-wheel steering angle for each of the steerable wheels as a function of at least one signal delivered by the operating means and as a function of at least one signal representing the actual trajectory of the vehicle. The trajectory controller is programmed so as to ensure consistency between the trajectory desired by the driver, effected by his actions on the operating component, and the actual trajectory, as may be observed by appropriate sensors (examples of which include a longitudinal speed sensor, a transverse acceleration sensor and a yaw sensor).
It is also an object of the present invention, independently of the previous object, to provide the driver of a vehicle with a specific operating component, which makes it possible to cause transverse translation of the vehicle at constant heading. This operating component is independent of the operating component for turning the vehicle, that is to say, independent of the yaw control (change of heading). The intended object is to provide an operating device which is as familiar as possible to a driver, who is already accustomed to the use of a steering wheel for acting on the trajectory of his vehicle, while also providing the opportunity for improvement.
Accordingly, the present invention retains the use of a first operating component of the xe2x80x9csteering wheelxe2x80x9d type for applying changes of direction to the vehicle. As a reminder, a change of direction corresponds to a change of heading. The instructions for changing the direction of the vehicle are given conventionally, that is to say, by applying a rotation to this first component. In order to decouple the controls for transverse translation of the vehicle, at constant heading, from the controls for changing the direction of the vehicle (change of heading), the present invention proposes to equip the operating device with a specific operating second component for applying a transverse displacement to the vehicle at constant heading (that is to say, without yaw).
Consequently, the invention relates to an operating device for acting on the trajectory of a vehicle, all of whose road wheels are steerable wheels, with displacement instructions for the steerable wheels being transmitted by electrical means, the operating device having a first operating component for applying a yaw movement to the vehicle, the first operating component essentially having a rotary shaft to which are secured two handles which are arranged at a certain distance from the rotary shaft, which rotary shaft is provided with at least one angle-of-rotation sensor and with a means for returning to a straight-line position, and having a second operating component for applying a yaw-free transverse displacement to the vehicle.